1. Field of the invention
This invention relates to improvements in rotating cutter tools for making holes by trepanning or by drilling.
2. Description of the prior art
Conventional cutter tools of this kind comprise cutting blades and support strips forming support surfaces for defining slots for lubricant films between the support surfaces and the wall of the hole made. Rotating cutter tools of this type are employed in deep-well drilling, i.e., drilling at a depth greater than three times the diameter of the bore. The support surfaces serve to avoid lateral movement of the tool away from the axis of the bore during drilling. At least two support surfaces are formed by support strips in prior art cutter tools of this kind. Uneven wearing of these support strips and of the cutting edges cannot be avoided for conventional tools; this in turn, leads to a tendency of the tool toward lateral movement, a shorter life, and development of vibrations during drilling. This results in bores out of round having wavy bore surfaces for which exact tolerances cannot be maintained.
It is the purpose of the present invention to obviate the aforementioned difficulties by providing a rotating cutter tool having at least two cutting blades and at least three support surfaces with which round, smooth bore holes can be drilled with extremely small tolerances.